Someone showed this to me a few years ago, it shows a lot of things from Warcraft 1 which never made it into the game. Also, if you use a hex editor on Warcraft 1 data files, you can see that they included a section for a dragon, but never implemented it.

My friend Hallfiry is researching the history of Blizzard and its games, and he has uncovered quite a lot of pre-release Warcraft: Orcs & Humans screenshots. You can view some of them here.

Apparently, the concept of roads (which was obviously modelled after concrete slabs in Dune II) was dropped at some point but later reintroduced back into the game. Also stone was one of the resources at a certain stage of development.

Also there's an early public demo version of Warcraft which has a different sprite and icons for Human Barracks, as well as some other differences. Comparison screenshots can be found here.